The present invention generally relates to signal pickup devices in rotary recording medium reproducing apparatus, and more particularly to a signal pickup device in which the length of a metal ribbon connecting a reproducing stylus and the resonator is suitably determined so that a most lowered position of the reproducing stylus is at a height position in which the stylus does not make contact with a turntable, to prevent possible damage to the reproducing stylus when the rotary recording medium reproducing apparatus is set to a reproducing mode in the state where a rotary recording medium is not placed onto the turntable.
Conventionally, apparatus for reproducing rotary recording mediums of a so-called electrostatic capacitance type have been reduced to practical use. In this reproducing apparatus, a reproducing stylus makes contact with and slides along a recorded track of the rotary recording medium (hereinafter simply referred to as a disc) in which an information signal such as a video signal is recorded as variations in geometrical configuration, to reproduce the recorded signal as variations in electrostatic capacitance between the disc and an electrode of the reproducing stylus. An example of a signal pickup device used in the above type of a reproducing apparatus consists of a cantilever rotatably supported at a base part side and having a reproducing stylus at the tip end thereof for making contact with and sliding against the disc surface to reproduce a signal, a mechanism for rotating the cantilever upon reproduction and causing the reproducing stylus to make contact with and slide against the disc, a resonator, and a metal ribbon for connecting the reproducing stylus and the resonator in a state where the reproducing stylus can freely move upwards and downwards. The information signal is picked up by virtue of the fact that the resonance frequency of the resonator varies in accordance with the variation in geometrical configuration of the disc surface. In this signal pickup device, the length of the metal ribbon is set so that the metal ribbon is in a slightly curved and bent state when the reproducing stylus makes contact with and slides against the disc surface. Accordingly, the reproducing stylus can freely move upwards and downwards, and the metal ribbon does not interfere with the movement of the reproducing stylus as the reproducing stylus follows and traces the fluctuations in the rotating plane of the disc.
On the other hand, the disc is accommodated within a case with a lid, and the disc is placed onto the turntable within the reproducing apparatus by a loading operation in which the case accommodating the disc is inserted into and then pulled out (extracted) from the reproducing apparatus. Moreover, the reproducing apparatus detects the loading of the disc onto the turntable, indirectly, by detecting that the lid of the case is locked at an innermost part of the reproducing stylus. Hence, in a case where an insertion and extraction operation is performed with respect to an empty case provided with a lid not accommodating a disc, for example, or in such a case where the case is extracted in a state accommodating the disc although the lid is locked within the reproducing apparatus by the insertion and extraction of a normal case accommodating a disc, the reproducing apparatus detects that the disc is loaded, although in reality, the disc may not be loaded onto the turntable. Under such circumstances, the reproducing apparatus operates in a manner identical to when a disc is loaded onto the turntable. Thus, the signal pickup device moves towards the turntable, and the reproducing stylus is lowered. Conventionally, special considerations were not given with respect to the length of the metal ribbon and the size and shape of the turntable. Therefore, the reproducing stylus is lowered below a reference height position during reproduction, into a position where the reproducing stylus makes contact with the upper surface of the turntable. This can instantly damage the reproducing stylus to such extent that the reproducing stylus cannot be used again, when the reproducing stylus rubs against the upper surface of the turntable.